Development Of Additive Manufacturing Technology Research Articles

Topology optimization of thin-walled tubes filled with lattice structures

Thin-walled tubes filled with ultra-light materials have attracted much attention due to excellent energy absorption characteristics. With the development of additive manufacturing technology, it is allowed to manufacture structures with complex geometry shapes as new filled materials. In this study, complex proportional assessment (COPRAS) and discrete optimization algorithm were proposed to design and optimize the topology of thin-walled tubes filled with lattice structures. Firstly, the finite element model verified by experiment was adopted to investigate the influence of cross-sectional configurations and octet truss lattice filling distributions on crashworthiness of hybrid structures. The results show that the cross-sectional configuration has a greater effect on specific energy absorption (SEA) and the lattice filling distribution has a greater effect on peak crushing force (PCF). Then, COPRAS was used to sort the crashworthiness of hybrid structures with different topologies and select the optimal solution. It was found that C3-L4 structure had the best crashworthiness among all design schemes, indicating that the better crashworthiness can be obtained by filling the lattice in the four corner regions of tube or increase the number of cells in corner regions. Finally, the discrete optimization algorithm based on successive orthogonal arrays was adopted to further improve the crashworthiness of hybrid structure. It was found that the thin-walled tubes with different thickness had greater energy absorption capacity than those with the same thickness. Hence, the method proposed in this paper can become an effective way for topology optimization of crashworthiness.

Effect of slot-shaped pins on heat transfer performance in the extended jet impingement cooling

In this study, effects of heat transfer performance on the roughened target surface with slot-shaped pins (SSP) were numerically investigated using an in-line array of extended jet impingement cooling models. The influence of pin heights on convective heat transfer for variable nozzle lengths, different pin arrangements, and Reynolds numbers (Re) in a rectangular channel flow was examined. The pins were located in a staggered and circular pattern. The numerical solution procedure has been verified by comparing numerical results with the available experimental data in the literature. The simulations were conducted with shear stress transport k-ω with low-Re correction turbulence model considering boundary conditions. The numerical model reasonably predicted heat transfer and pressure drop for flat plates and roughened plates with pins. Average Nusselt numbers on the surface were determined numerically using the model validated with experimental data for different dimensionless pin heights Hp/Dj (0.167, 0.417, and 0.667), various pin arrangements (R1, R2, R3), dimensionless nozzle lengths Gj/Dj (1.0, 2.0, and 6.0), and Re numbers (16250, 27100, and 32500). Numerical results were compared with the orifice plate; in other words, the conventional jet impinging configuration (Gj/Dj= 6.0 and Hp/Dj= 0). When the system's flow characteristics and performance evaluation criterion were considered, optimum geometric parameters for all Re were determined as Hp/Dj= 0.167 and R1_Gj/Dj= 1.0. Obviously, pin-roughened surfaces strongly affect the mean convective heat transfer and the homogeneity of the local heat transfer in extended jet impinging cooling systems. In this way, the negative effect of thermal stresses on the interested surface can be reduced, and the life of the material can be extended. Since the development of additive manufacturing technologies makes it possible to use these geometries in the internal cooling channels of gas turbine blades, a significant contribution will be made to the literature as a result of this study.

Non-linear dynamic finite element analysis of micro-strut lattice structures made by laser powder bed fusion

The development of additive manufacturing technologies enables the production of a new type of porous materials for the absorption of mechanical energy. These are, for example, metallic lattice structures produced by laser powder bed fusion. The structures can be made from a wide range of alloys, achieve high specific energy absorption, and can be manufactured as hybrid parts with conventional bulk components. To effectively develop lattice structures, it is necessary to complement experimental tests with simulations using the finite element method (FEM) performed under conditions of increased loading velocities. Therefore, this study focuses on the development of the FEM modelling strategy that reflects the effect of strain rate sensitivity of the base material (SS316L) and the most significant geometrical imperfections of the manufacturing process. The strain rate is reflected by the Cowper-Symonds constitutive law, which parameters are determined by the dynamic tensile test on Hopkinson split bars. The imperfections are captured by optical digitalization. The significance of the Cowper-Symonds parameters and geometric imperfections are studied independently, whereas agreement with the experiment is observed. Tests are performed for several lattice structures with different strut orientations and velocities to evaluate the versatility of the proposed approaches. A good correlation between computational and experimental results in terms of energy absorption is found for structures with an experimentally determined strut diameter and the proposed Cowper-Symonds input parameters.

Fracture of Honeycombs Produced by Additive Manufacturing

Lattice materials, such as honeycombs, are remarkable in their ability to combine high stiffness, strength and toughness at low density. In addition, the recent and pervasive development of additive manufacturing technologies makes it easier to produce these cellular materials and opens new possibilities to improve their properties by implementing small modifications to their microstructure. Such developments open new opportunities towards the design of new classes of architectured materials. For example, recent computational studies have shown that honeycombs with lattice density gradients have a fracture energy under tensile loading up to 50% higher than their uniform counterparts. The aim of this study is to provide experimental evidence for these promising numerical results. To achieve this, single-edge notched tension specimens, with a honeycomb lattice structures, were manufactured by stereolithography using a ductile polymer resin. The performances of three different honeycombs were compared: (i) a uniform sparse lattice, (ii) a uniform dense lattice, and (iii) a gradient lattice with alternating bands of sparse and dense lattices. The results indicated that specimens with a density gradient may achieve a work of fracture per unit volume that is up to 79% higher than that of a uniform lattice.

Effect of laser scan pattern in laser powder bed fusion process: The case of 316L stainless steel

Recent developments in additive manufacturing technologies allows generating different type of microstructure by modifying the additive manufacturing parameters. Indeed, with the laser powder bed fusion process, the laser power, energy density or laser scan strategies are such of parameters which affect size, morphology and orientations of grains. This allows to build microstructures which were no accessible with conventional processes. Furthermore, the control of laser scan strategies allows to significantly reducing the size and density of defects inherent to the process (gas pores, lack of fusion). These advances make it possible to study the role of microstructure and defect on fatigue crack initiation behaviour for additive manufactured materials. This paper aims to take this opportunity for studying the 316L stainless steel built with the laser powder bed fusion process.

Ti-6Al-4V lattices obtained by SLM: characterisation of the heterogeneous high cycle fatigue behaviour of thin walls.

Architectured materials are attracting increasing interest since a few years, achieving numerous excellent specific properties compared to fully dense materials. The transport industry sector see periodic assemblies of elementary cells, called lattices, as a solution to lighten structures. This is made possible by the development of Additive Manufacturing technologies (AM). Among the numerous advantages of AM, these processes allow to create a wide range of porous cell topologies, and to tailor their complex geometry with the desired properties. However, understanding their fatigue properties is essential to validate their long-term use in load-bearing parts.The FA process plays an important role in fatigue life, as it generates residual stresses, heterogeneous microstructure, as well as surface and volume defects (roughness, gaz porosities, lack of fusion porosities), which are preferred sites for fatigue crack initiation. The fatigue life of these structures also depends strongly on their geometry, which, due to their complexity, induces scale and stress gradient effects.Recent studies have recognize thin-walls TPMS (Triply Periodic Minimal Surfaces) structures as the most promising structures for fatigue resistance, especially the gyroid geometry, compared to conventional strut-lattices.The first aim of this work is to characterise the major parameters influencing fatigue life at the lattice scale. Roughness, microstructure will be discribed on a lattice specimen, and topology effect on stress distribution will be numerically quantified. In order to understand the influence of these parameters, and identify the critical region for fatigue life, this work focuses on the local thin-wall scale. Here, the aim is to characterise the high cycle (HCF) fatigue heterogeneous response of Ti-6Al-4V thin-walls manufactured, characterising localy the HCF behaviour of a TPMS lattice structure (R=0.1; uniaxial tension loading, N=1.106, f=40Hz).

Multi-scale Topology Optimization Using FFT-based Homogenization with Elasto-plastic Material

Thanks to the development of additive manufacturing technology, it is becoming possible to produce materials with desired mechanical properties defined by their periodic microstructures. Multi-scale topology optimization has been paid attention to in many engineering fields to design optimal microstructures. However, its high computational cost prevents practical use, such as high-resolution 3D analysis for precision modeling and non-linear analysis assuming actual materials. In this study, to solve this problem, we focus on the homogenization approach using fast Fourier transform and develop a new optimization method with fast computing speed and low memory requirement. By performing sample analyses, we demonstrate the validity and efficiency of the proposed method.

Development of Additive Manufacturing Technology and Industry in China

As an emerging manufacturing technology, additive manufacturing (AM) has become one of the fastest developing technologies in the advanced manufacturing field with the continuous expansion of its applications. The development of AM industry provides a valuable opportunity for the development of modern manufacturing and the transformation and upgrading of traditional manufacturing. In this paper, developmental trends of the AM technology and industry in China and abroad are systematically summarized, and problems faced by China’s AM industry are analyzed, including inadequate research and development capabilities regarding common technologies and basic devices, lack of effective patent layout for the international market, and insufficient development of industrial scale and clusters. Focusing on a prospective layout of the AM industry, key development directions are proposed, including AM for biomedicine and medical devices, large-scale complex components, space, structural innovation, and new materials. Furthermore, several suggestions are put forward. First, an AM collaborative innovation mechanism should be established to support application innovation of enterprises. Second, special research plans on AM process reforms should be implemented to satisfy the demand for major high-end equipment. Third, the construction of regional AM industrial clusters should be promoted.

Environmental Impact for 3D Bone Tissue Engineering Scaffolds Life Cycle: An Assessment

With the development of additive manufacturing technology, 3D bone tissue engineering scaffolds have evolved. Bone tissue engineering is one of the techniques for repairing bone abnormalities caused by a variety of circumstances, such as injuries or the need to support damaged sections. Many bits of research have gone towards developing 3D bone tissue engineering scaffolds all across the world. The assessment of the environmental impact, on the other hand, has received less attention. As a result, the focus of this study is on developing a life cycle assessment (LCA) model for 3D bone tissue engineering scaffolds and evaluating potential environmental impacts. One of the methodologies to evaluating a complete environmental impact assessment is life cycle assessment (LCA). The cradle-to-grave method will be used in this study, and GaBi software was used to create the analysis for this study. Previous research on 3D bone tissue engineering fabrication employing poly(ethylene glycol) diacrylate (PEGDA) soaked in dimethyl sulfoxide (DMSO), and diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide (TPO) as a photoinitiator will be reviewed. Meanwhile, digital light processing (DLP) 3D printing is employed as the production technique. The GaBi program and the LCA model developed to highlight the potential environmental impact. This study shows how the input and output of LCA of 3D bone tissue engineering scaffolds might contribute to environmental issues such as air, freshwater, saltwater, and industrial soil emissions. The emission contributing to potential environmental impacts comes from life cycle input, electricity and transportation consumption, manufacturing process, and material resources. The results from this research can be used as an indicator for the researcher to take the impact of the development of 3D bone tissue engineering on the environment seriously.

A Numerical Study on 3D Printed Cementitious Composites Mixes Subjected to Axial Compression

Aptly enabled by recent developments in additive manufacturing technology, the concept of functionally grading some cementitious composites to improve structural compression forms is warranted. In this work, existing concrete models available in Abaqus Finite Element (FE) packages are utilized to simulate the performance of some cementitious composites numerically and apply them to functional grading using the multi-layer approach. If yielding good agreement with the experimental results, two-layer and three-layer models case combinations are developed to study the role of layer position and volume. The optimal and sub-optimal performance of the multi-layer concrete configurations based on compressive strength and sustained strains are assessed. The results of the models suggest that layer volume and position influence the performance of multi-layer concrete. It is observed that when there exists a substantial difference in material strengths between the concrete mixes that make up the various layers of a functionally graded structure, the influence of position and of material volume are significant in a two-layer configuration. In contrast, in a three-layer configuration, layer position is of minimal effect, and volume has a significant effect only if two of the three layers are made from the same material. Thus, a multilayered design approach to compression structures can significantly improve strength and strain performance. Finally, application scenarios on some structural compression forms are shown, and their future trajectory is discussed.

Additive Manufacturing Technologies and Its Future in Industrial Applications

Additive manufacturing technologies have developed rapidly in the last ten years and have become a technology with significant advantages compared to traditional manufacturing. Depending on discovering new materials and techniques, additive manufacturing technologies also develop and become more economical and sustainable technology. The widespread use of this technology in industrial areas has accelerated development and contributed to increased product quality. However, to ensure the development and continuity of this technology, it is necessary to reduce the production costs, increase the quality and accelerate the production processes. These processes also trigger competition and accelerate the development of technology. The areas that additive manufacturing technologies are mostly applied can be grouped as aerospace, biomedical, smart technologies, and other industrial applications. The fact that these areas are popular research areas also accelerates the development of additive manufacturing technologies. In this review, additive manufacturing technologies frompast to present, advantages and disadvantages of these technologies, aspects that need to be developed, and industrial applications are examined and explained. When the studies on additive manufacturing technologies and industrial applications are examined, it is seen that this technology has a wide usage area. With the use of additive manufacturing technologies, previously encountered in prototypes and special applications, in automotive, biomedical, and smart technologies, it is seen that they have begunto take place more in people's daily lives.

Cruciate-Ligament-Inspired Compliant Joints: Application to 3D-Printed Continuum Surgical Robots.

The rapid development of additive manufacturing technology makes it possible to fabricate a patient-specific surgical robot in a short time. To simplify the assembly process of the printed robotic system, compliant-joint-based monolithic structures are often used as substitutes for rigid-link mechanisms to realize flexible bending. In this paper, we introduce a cruciate-ligament-inspired compliant joint (CLCJ) to improve the bending stability of the 3D-printed continuum surgical robots. The basic structure of the tendon-driven CLCJ mechanism and its kinematic model were described in detail. The bending performance of CLCJ was also successfully evaluated by FEM simulation and experimental tests. Besides, a prototype of CLCJ-based surgical robotic system was presented to demonstrate its application in 3D-printed continuum surgical robots.

Structural Design Method for Constructions: Simulation, Manufacturing and Experiment

The development of additive manufacturing technology leads to new concepts for design implants and prostheses. The necessity of such approaches is fueled by patient-oriented medicine. Such a concept involves a new way of understanding material and includes complex structural geometry, lattice constructions, and metamaterials. This leads to new design concepts. In the article, the structural design method is presented. The general approach is based on the separation of the micro- and macro-mechanical parameters. For this purpose, the investigated region as a complex of the basic cells was considered. Each basic cell can be described by a parameters vector. An initializing vector was introduced to control the changes in the parameters vector. Changing the parameters vector according to the stress-strain state and the initializing vector leads to changes in the basic cells and consequently to changes in the microarchitecture. A medium with a spheroidal pore was considered as a basic cell. Porosity and ellipticity were used for the parameters vector. The initializing vector was initialized and depended on maximum von Mises stress. A sample was designed according to the proposed method. Then, solid and structurally designed samples were produced by additive manufacturing technology. The samples were scanned by computer tomography and then tested by structural loads. The results and analyses were presented.

Multi-scale analysis for 3D printed continuous fiber reinforced thermoplastic composites

With the development of additive manufacturing technology, the designing and fabrication of continuous fiber reinforced thermoplastic composites (CFRTPCs) are concerned and studied more extensively. In this paper, both melting-deposition-cooling manufacturing process and the mechanical properties of 3D printed CFRTPCs are simulated. First, theoretical and numerical models of the 3D printing process for CFRTPCs are proposed, which take the resin infiltration, temperature changes and resin curing into account. Second, influences of the stacking method, the aspect ratio of the oval bead, the width and height between beads on resin infiltration and density of 3D printed CFRTPCs are analyzed. Finally, the mechanical properties of 3D printed CFRTPCs are predicted using multi-scale simulation methods. This work provides the simulation method and theoretical basis for the design and evaluation of 3D printed CFRTPCs.

Compression Experiment and Failure Analysis of Additive Manufactured Multi-Layer Lattice Sandwich Structure

The rapid development of additive manufacturing technology provides a new opportunity for the fabrication and research of multi-layer lattice sandwich structures, and thereby some excellent performances can be further discovered. Based on the manufacturing-experiment-analysis technical route, the failure mode of the additive manufactured aluminum multi-layer alloy lattice sandwich structure under quasi-static compression is systematically studied in this paper. Through the combination of experimental observation and finite element analysis, the complex failure mechanism of the multi-layer lattice sandwich structure is revealed. The results show that the multi-layer lattice sandwich structure under quasi-static compression conditions mainly manifests as a layer-by-layer failure mode of the internal lattice structure, which includes the yield, plastic buckling and material damage. At the same time, in comparison with the force–displacement curve and the structural deformation in the key locations, the analysis accuracy of the finite element model can be verified by the compression experiment. Based on the verified finite element model, the most significant influence of different face panel thicknesses, as well the rod radiuses and tilting angles on the energy absorption (EA) is identified via sensitivity analysis. Furthermore, size factors on the structural EA are revealed. This study can provide a helpful guidance for the design of multi-layer lattice sandwich structures in practical applications.

Additively manufactured mechanical metamaterials based on triply periodic minimal surfaces: Performance, challenges, and application

Lattice structures with architecture based on triply periodic minimal surfaces (TPMS) have recently attracted much attention due to their mathematically controlled topologies, which give rise to predefined and fascinating mechanical properties. Such materials with topology-dependent properties are generally known as “metamaterials.” The research on the TPMS-based metamaterials was restricted to theoretical knowledge until the recent development of additive manufacturing technology (AM). Herein, the design, properties, challenges, and applications, of TPMS-based mechanical metamaterials are reviewed. This review provides the researcher with a collective resource of numerical and experimental data for the AM of TPMS-based structures.

A review of additive manufacturing applications in ophthalmology.

Additive Manufacturing (AM) capabilities in terms of product customization, manufacture of complex shape, minimal time, and low volume production those are very well suited for medical implants and biological models. AM technology permits the fabrication of physical object based on the 3D CAD model through layer by layer manufacturing method. AM use Magnetic Resonance Image (MRI), Computed Tomography (CT), and 3D scanning images and these data are converted into surface tessellation language (STL) file for fabrication. The applications of AM in ophthalmology includes diagnosis and treatment planning, customized prosthesis, implants, surgical practice/simulation, pre-operative surgical planning, fabrication of assistive tools, surgical tools, and instruments. In this article, development of AM technology in ophthalmology and its potential applications is reviewed. The aim of this study is nurturing an awareness of the engineers and ophthalmologists to enhance the ophthalmic devices and instruments. Here some of the 3D printed case examples of functional prototype and concept prototypes are carried out to understand the capabilities of this technology. This research paper explores the possibility of AM technology that can be successfully executed in the ophthalmology field for developing innovative products. This novel technique is used toward improving the quality of treatment and surgical skills by customization and pre-operative treatment planning which are more promising factors.

An adaptive slicing approach for processing STL massive data model in batches based on layer merging

Slicing is one of the core parts of the additive manufacturing software system, which completes the function of transforming the 3D model into a 2D profile. The adaptive slicing algorithm uses different layer thicknesses for layering in different areas according to the changes in the geometry of the mesh model. Where the model is more complex and the curvature changes a lot, a smaller layer thickness is used to approximate the model. In areas of large curvature of the model, maximum layer thickness is used to improve printing efficiency. With the development of additive manufacturing technology, grid model files such as STL have become larger and larger, and the amount of data needed to be processed by slicing software has increased dramatically. Existing slicing software is limited by computer hardware and cannot process massive data model. It greatly limits the development of additive manufacturing technology, so it is urgent to propose a new method to solve the rapid stratification of mass data model. In this paper, we proposed an adaptive slicing approach for processing STL massive data model in batches based on layer merging. At the same time, it is compared with the fixed-layer thickness slicing method, which shows that the algorithm can improve printing efficiency under the premise of ensuring accuracy.

Mechanical and Structural Evaluation of the PA12 Desktop Selective Laser Sintering Printed Parts Regarding Printing Strategy.

Despite the dynamic development of additive manufacturing technologies, including selective laser sintering (SLS), there is still limited information on the impact of key factors in printing strategy, on the properties of three-dimensional (3D) printed parts. Such factors, such as the orientation of printed layers toward the powder bed or elements target dimensions, seem to be particularly important, from both a mechanical and a structural point of view. Besides, the scientific articles mainly focus on the analysis of one type of loading condition in the samples, that is, the uniaxial tensile test, which were printed on industrial SLS printers. This is a considerable limitation because very often not only tensile forces but also compressive forces act on the structural elements. Therefore, this study aimed at evaluating the influence of desktop SLS printed parts' orientation and diameter on their structural and mechanical parameters. The mechanical properties of samples printed from PA12 powder on the desktop SLS 3D printer were tested in uniaxial tensile and compression tests, as well as structural properties were investigated. For the purposes of this article, 5 angular orientations of the samples in relation to the powder bed and three diameters of cylindrical samples were analyzed. The research has shown that in the case of samples subjected to tensile load, the printing strategy is important, and the best mechanical parameters are obtained for parts printed at an angle of 0°, that is, in the powder bed's plane. The highest values of mechanical parameters were obtained for a part oriented at an angle of 0°. In the case of the uniaxial compression test and structural parameters, the parts orientation turned out to be an insignificant factor affecting the tested parameters. However, the diameter of printed elements was proven to have a significant influence; the best geometric and dimensional representation was observed for parts biggest in size.

Additive manufacturing embraces big data

Additive manufacturing (AM) is a relatively novel method to fabricate 3D objects by adding layer-upon-layer materials. As one of the most anticipated techniques in recent years, AM already made advances in design, production, and supply chain process of the manufacturing industry. AM is a digital manufacturing technology in which a massive amount of data is generated during the process. Accordingly, obtaining useful information from these data to improve current AM technology becomes a challenge. Meanwhile, Big Data research provides an ideal solution for dealing with the massive data obtained from AM processes. Besides the contributions in the AM research and production, Big Data analysis methods can also be used to help designers and engineers by collecting valuable information from clients and customers. From a business perspective, the manufacturing sector will benefit from the established Big Data sharing platform to promote and popularize new products. On the other hand, customers will obtain desired commodities with the help of a new-type 3D printing service system. The goal of this article is to summarize the contributions from the existing literature in the AM and Big Data field and prospect how Big Data methods can offer a better future for AM technology. It also introduces recent developments in AM technology combined with the internet of things (IoT), cloud, and cybersecurity. Future directions in AM and Big Data, which include AM data unification, completed AM data-sharing platform, and smart AM production process is pointed out as well.